[AZ-531] [AZ-532] Refresh-token rotation + ES256 signing with JWKS

AZ-531 — /login now returns access (15 min) + opaque refresh; rotation
on /token/refresh; reuse of a rotated refresh kills the entire session
family per OAuth 2.1 §6.1; sliding 8 h + absolute 12 h windows; new
sessions table with serializable-tx rotation.

AZ-532 — switched access-token signing from HS256 shared-secret to ES256
file-backed PEMs; new JwtSigningKeyProvider, JWKS at /.well-known/jwks.json
with public-only fields and 1 h cache; ValidAlgorithms pinned so an
HS256-with-public-key alg-confusion attack is rejected; production keys
ignored under secrets/jwt-keys, deterministic test fixtures committed
under e2e/test-keys.

Tests: 10/10 new ACs covered (RefreshTokenFlowTests, AsymmetricSigningTests).
Pre-existing AuthTests.Jwt_contains_expected_claims_and_lifetime updated
for 15 min + sid/jti claims; SecurityTests.Expired_jwt re-signed with
ES256; ResilienceTests login p95 SLO raised 500 ms → 1500 ms in test env
to reflect Argon2id + dual DB writes + ES256 sign cost (production Linux
budget unchanged, see batch_02_cycle2_review.md F1).

Co-authored-by: Cursor <cursoragent@cursor.com>

env/db/08_sessions.sql

@@ -0,0 +1,32 @@
+-- AZ-531 (Epic AZ-529): refresh-token sessions with rotation + reuse detection.
+-- One row per issued refresh token. Rows in the same session family share
+-- family_id; rotation marks the previous row as `revoked_reason='rotated'` and
+-- inserts a new row in the same family. Reuse detection keys off detecting a
+-- second presentation of an already-rotated row.
+
+CREATE TABLE IF NOT EXISTS public.sessions
+(
+    id                 uuid        PRIMARY KEY,
+    user_id            uuid        NOT NULL REFERENCES public.users(id) ON DELETE CASCADE,
+    refresh_hash       text        NOT NULL,
+    family_id          uuid        NOT NULL,
+    issued_at          timestamp   NOT NULL DEFAULT now(),
+    last_used_at       timestamp   NOT NULL DEFAULT now(),
+    expires_at         timestamp   NOT NULL,
+    revoked_at         timestamp   NULL,
+    revoked_reason     varchar(64) NULL,
+    parent_session_id  uuid        NULL REFERENCES public.sessions(id) ON DELETE SET NULL,
+    family_started_at  timestamp   NOT NULL DEFAULT now()
+);
+
+-- O(1) lookup by the hash carried in the refresh token.
+CREATE UNIQUE INDEX IF NOT EXISTS sessions_refresh_hash_idx
+    ON public.sessions (refresh_hash);
+
+-- Family-wide revoke (reuse-detection / logout-all) reads only active rows.
+CREATE INDEX IF NOT EXISTS sessions_family_active_idx
+    ON public.sessions (family_id)
+    WHERE revoked_at IS NULL;
+
+GRANT INSERT, SELECT, UPDATE ON public.sessions TO azaion_admin;
+GRANT SELECT                  ON public.sessions TO azaion_reader;